The electronic structure and spectroscopy of the ionic dye ethidium bromide and related compounds are being investigated in an effort to understand the basis for the fluorescence enhancement which is observed when these compounds bind to nucleic acids by intercalation. Analogs of ethidium are being synthesized as part of this study and in an effort to enhance the resolution and fluorescence detection sensitivity of the dye buoyant density procedure for the isolation of closed circular DNA. Experiments with buoyant media other than CsCl are being performed as part of this study using PM2 DNA. The binding of ethidium to dinucleotides and defined polynucleotides and the resulting spectral and fluorescence changes are being studied.